At 120 volts, the most common household current in the United States, a 100-watt light bulb draws 0.83 amps. To calculate the amperage of a light bulb, one must divide the number of watts by the volts powering the circuit.
In order to reduce energy consumption, the 100-watt light bulb is no longer available in the United States. In addition, light bulbs between 40 watts and 100 watts must meet the requirement that they are a minimum of 30 percent more efficient. This reduction in wattage also results in a reduction in amperage for light bulbs so that the replacement bulbs are safe for use with existing wiring.